Some questions from someone who is fairly ignorant. 1) Is it really worthwhile to prevent rot, when instead decaying trees can just be placed somewhere to hold

Some questions from someone who is fairly ignorant. 1) Is it really worthwhile to prevent rot, when instead decaying trees can just be placed somewhere to hold the carbon underground? 2) Does the higher metal content or change to C4-style plants lead to any macroscopic changes in the wood, especially with regards to strength, workability or warping/expansion? 3) Is there a reason you focused on decay-resistence over the other areas you expressed, specifically nitrogen fixation, which seems like it would get faster results on the "trees as carbon sinks" goal?